Conventionally, in manufacturing electrophotographic toners, a charge controlling agent is dispersed in a toner binder to control triboelectrification properties, i.e., a controlling agent is incorporated in a toner binder with coloring material and other additives followed by kneading and pulverizing to make the toner.
In this process, however, the triboelectrification property is not stable since it depends on the degree of dispersion of the charge controlling agent, and since the triboelectrification property depends on the charge controlling agent on the toner surface, any charge controlling agent inside of the toner does not influence triboelectrification. Additionally, the foregoing prior art process causes a loss of fixing performance as well as the mechanical strength of the binder resin. What is worse, since the charge controlling agent is in a state where it is mixed with coloring material, it is influenced by the triboelectrification property of the coloring material. Therefore, in manufacturing different colored toners, the type and quantity of charge controlling agent must be changed depending on the coloring material and results in high manufacturing costs. Additionally, this process can not be applied to a capsule toner having a core/shell structure.
Another toner manufacturing process is described in Japanese unexamined patent publication Nos. Sho 57-202547, 63-27853 and 63-27854 which disclose a process for manufacturing a toner by spray drying a polymer, which contains a charge controlling agent onto toner particles or coating this polymer combination on toner particles under conditions of heat and pressure.
The spray drying process, however, has the disadvantage in that the coating layer covers a plurality of toner particles simultaneously and enlarges the toner particle diameter. Even if the toners are screened afterwards, the yield of toner with a specified particle diameter is low. Additionally, there are problems with regard to safety and sanitation when using large quantities of organic solvent which may be required in the spray drying process.
The heat fixing coating process also has the disadvantage that it brings about adhesive coagulation of toner particles, which enlarges the toner particle diameter.
As for the process for fixing coating polymers to the toner particles by the process of employing pressure, there is a disadvantage in that when this process is applied to a capsule toner having a liquid core, the capsule is destroyed. There is no problem, however, if the pressure process is applied to toners having a hard core particle.
In Japanese unexamined patent publication No. Sho 60-173552, a toner manufacturing process is disclosed in which a toner is obtained by forming a coating layer consisting of a colorant and binder resin, magnetic particle and binder resin or conductive agent and binder resin on a toner core particle surface by means of a jet mill. In Japanese unexamined patent publication No. Sho 63-49766, a process is disclosed by which a toner particle surface is coated with thermoplastic resin by a distortion mixing process. Both of these processes, as is the case with the other prior art processes described above, have the disadvantage that the capsule structure of a capsule type toner having a liquid core which is employed in pressure fixing operations, is destroyed, although they are applicable in manufacturing hard toner core particles that are employed in heat fixing operations.
A toner manufacturing process is described in Japanese unexamined patent publication No. Sho 57-45558 in which the toner is obtained by dispersing toner core particles formed by polymerization in an aqueous latex solution followed by forming a coating layer on the particle by adding a water soluble inorganic salt and precipitating microparticles on the toner core particle. This process, however, has the disadvantage that triboelectrification depends on environmental changes to a large extent, influenced by interfacial active agents or inorganic salts remaining on the microparticles. Triboelectrification declines with particles manufactured in this way, especially in an environment of high temperature and high humidity and this process also has the disadvantage that the adhesive properties between toner core particles and polymer microparticles is poor.
A process for adhering a polymer of a monomer having triboelectrification properties to a toner particle is described in Japanese unexamined patent publication Nos. Sho 62-227161 and 62-227162. These references describe the way in which a polymeric monomer having a charge controlling moiety is graft polymerized after being chemically bonded to a toner particle surface. A typical connected molecule in this regard is ethylene glycol dimethacrylate. As the charge controlling moiety is localized on the toner surface, the fixing property of the toner binder is not lost and the toner binder is not easily influenced by the triboelectrification property of coloring materials. This process, however, has the disadvantage in that the toner binder undergoes this reaction in two steps which takes time and requires additional labor which consequently leads to higher costs.
Accordingly, it is an object of the present invention to overcome these and other difficulties encountered in the prior art.
It is a further object of the present invention to provide a process for manufacturing an electrophotographic toner in which the aforesaid disadvantages are overcome without losing the fixing performance and mechanical strength of the binder resins employed in manufacturing such toners.
It is a further object of the present invention to provide a process for manufacturing an electrophotographic toner in which the toner is not influenced by the triboelectrification property of the coloring material.
It is also an object of the present invention to provide a process for manufacturing an electrophotographic toner in which the adhesive coagulation of the toner particles is eliminated or substantially minimized so that the particle diameter of the resultant toner does not increase or it substantially controlled.
It is a further object to the present invention to provide a process for manufacturing an electrophotographic toner in which the toner has excellent adhesive properties with regard to the core particle and is free or substantially free of chemically reactive groups and further can be manufactured by a relatively uncomplicated process.
It is a further object of the present invention to provide a process for manufacturing an electrophotographic toner which is applicable to capsule type toners having a liquid core wherein the resultant toner has good stability against environmental change in a triboelectrification process.
These and other objects have been achieved according to the present invention.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be apparent to a person with ordinary skill in the art from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.